5/25/2021

ROV surveys

  • 2008 San Juan Islands
  • 2010 San Juan Islands
  • 2015-16 Puget Sound
  • 2018 San Juan Islands
  • 2018 Vector Survey (Strait of Georgia)
  • 2018 Gulf Islands Survey

Uses of ROV data for 5-year review

  • As an index of abundance for assessment model
    • Single time point of absolute abundance across entire DPS (as in the case of Hood Canal)
    • Time series of abundances from the same geographic area (as in the case of the San Juan Islands)
  • As an index of abundance to compare with reference points from the assessment model
  • To stress how repeated ROV surveys would allow us to track population dynamics without needing to do a formal assessment

What is the selectivity of ROV surveys?

Key to contextualizing abundance estimates

  • What types of individuals are seen by the ROV?
  • What proportion of these individuals are seen by the ROV?

Calculating abundance

The mean stratum density (\(\overline{D_s}\)) for a given taxon was the the sum of the individual transect densities divided by the number of transects (\(N_s\)):

\[ \overline{D_s} = \frac{\sum\limits_{i=1}^N D_i} {N_s} \] Total abundance (\(P\)) in numbers of individuals was the product of the stratum surface area (\(SA_s\)) and the mean taxon density (\(\overline{D_s}\)), with variance calculated as the product of the square of the surface area and the variance of mean stratum density:

\[ P_s = SA_s\overline{D_s};Var(P_s) = SA_s^2Var(\overline{D_s}) \]

Maximum entropy models

  • Machine learning method used to predict habitat suitability for target species
  • Maximum entropy used for 2015-16 Puget Sound, 2018 SJI, 2018 Gulf Islands, and 2018 Vector Surveys
  • Habitat suitability determined based on combination of previous occurrences and habitat characteristics/variables
    • Previous occurrences: Yelloweye and canary for 2015-16 Puget Sound Survey, only Yelloweye for other surveys
    • Habitat variables: Depth, roughness, and bottom current speed
  • Output from maximum entropy model: probability distribution (PD) map for each species, where each cell is assigned a probability of suitable habitat (not fish presence) based on the retained input variables.
    • Different strata determined by ranges of probabilities
  • 2018 Vector Survey (Strait of Georgia) included different habitat variables (?)

2015-16 Puget Sound Survey

2015-16 Puget Sound

non-Hood Canal

  • Survey strata: “High” (>50%), “Medium” (25-50%), “Low” (<25%)
    • High stratum
      • 363 transects
      • 9,288 hectares
      • 25 yelloweye
    • Medium + Low strata
      • 244 transects
      • 1,058,427 hectares
      • 0 yelloweye
  • Population estimate: 6,285 (CV = 29.5%)

Hood Canal

  • Survey strata: “High” (>50%), “Medium” (25-50%), “Low” (<25%)
    • High stratum
      • 152 transects
      • 4,486 hectares
      • 37 yelloweye
    • Medium + Low strata
      • 46 transects
      • 120,637 hectares
      • 0 yelloweye
  • Population estimate: 14,699 (CV = 22.9%)

2008 SJI ROV survey

  • Rocky habitat identified using MBES (multibeam echosounder)
  • Survey strata: “Shallow rock” and “Deep rock”
    • Shallow rock
      • 136 transects
      • 7,860 hectares
      • 1 yelloweye
    • Deep rock
      • 71 transects
      • 4,150 hectares
      • 38 yelloweye
  • Population estimate: 47,407 (CV = 24.8%)

2010 SJI ROV survey

  • Systematic grid used to determine transect locations; higher density of transects in Western SJI because of previous observations
  • Survey strata: “Eastern SJI” and “Western SJI”
    • Eastern SJI
      • 55 transects
      • 50,850 hectares
      • 0 yelloweye
    • Western SJI
      • 111 transects
      • 53,164 hectares
      • 16 yelloweye
  • Population estimate: 114,494 (CV = 44.0%)

2018 SJI ROV survey

  • Maximum entropy model
  • Survey strata: “High” (>25%) and “Low” (<25%)
    • High stratum
      • 51 transects
      • 6,036 hectares
      • 14 yelloweye
    • Low stratum
      • 9 transects
      • 102,115 hectares
      • 0 yelloweye
  • Population estimate: 19,059 (CV = 33.4%)

2018 Gulf Islands survey

  • Maximum entropy model
  • Survey strata: “High” (>50%), “Medium” (25-50%), “Low” (<25%)
    • High stratum
      • 40 transects
      • 6,070 hectares
      • 49 yelloweye
    • Medium stratum
      • 17 transects
      • 21,462 hectares
      • 4 yelloweye
    • Low stratum
      • 11 transects
      • 76,206 hectares
      • 0 yelloweye
  • Population estimates:
    • High stratum: 83,783 (CV = 34.3%)
    • Medium stratum: 58,887 (CV = 71.8%)

2018 Vector survey

  • Maximum entropy model
  • Survey strata: “High”, “Low”
    • High stratum
      • 84 transects
      • 92,031 hectares
      • 198 yelloweye
    • Low stratum
      • 1 transect
      • 816,993 hectares
      • 0 yelloweye
  • Population estimate: 1,613,716 (CV = 14.3%)

ROV abundance results

survey area year abundance CV
2008 San Juan Islands San Juan Islands 2008 47,407 25
2010 San Juan Islands San Juan Islands 2010 114,494 33
2015-16 Puget Sound Puget Sound Proper (excluding Hood Canal) 2015, 2016 6,285 29
2015-16 Puget Sound Hood Canal 2015, 2016 14,699 23
2018 San Juan Islands San Juan Islands 2018 19,059 33
2018 Gulf Islands - High Stratum Gulf Islands (Inside) 2018 83,783 34
2018 Gulf Islands - Medium Stratum Gulf Islands (Inside) 2018 58,887 72
2018 Vector Strait of Georgia (CA) 2018 1,613,716 14